1. Field of the Invention
The present invention relates to a method for production of an interposer for mounting a semiconductor element, where the interposer is used in mounting a semiconductor element onto a motherboard.
2. Description of the Related Art
In recent years, electronic devices equipped with semiconductor elements have become increasingly more compact and lightweight, and this trend has led to the development of the chip-size package (CSP) in which the semiconductor element is mounted on a circuit board, termed an interposer (namely, a semiconductor element mounting interposer), that has substantially the same dimensions as the semiconductor element, which package is then mounted on the motherboard.
Semiconductor element mounting interposers of this type are produced in the manner depicted in FIGS. 3A to 3D.
First, on an insulating base film 31 is formed a conducting circuit 34 that includes motherboard connecting electrodes 32 for interconnection with the motherboard, and plated leads 33 providing conduction paths to the motherboard connecting electrodes 32 to permit electroplating of the motherboard connecting electrodes 32, as in FIG. 3A. The plated leads 33 are in electrical connection with continuous conductors 31a situated at the two edges of insulating base film 31.
The semiconductor element mounting interposer is also provided with through-holes 35 which lead the motherboard connecting electrodes 32 to a semiconductor element (not shown) on the backside.
Next, the conducting circuit 34 is subjected to a electroplating process to deposit an electroplated metal layer 36 covering at least the motherboard connecting electrodes 32, as in FIG. 3B.
Next, using a die, the plated leads are severed by making holes 37 in proximity to the motherboard connecting electrodes 32 so as to make the plated leads 33 as short as possible, as in FIG. 3C. Where needed, the continuous conductors 31a situated at the two edges of the insulating base film 31 are trimmed, as in FIG. 3D.
The reason for cutting the plated leads 33 in proximity to the motherboard connecting electrodes 32 as in FIG. 3C is as follows.
Where the plated leads 33 in electrical connection with the motherboard connecting electrodes 32 on insulating base film 31 have considerable lengthwise extension, since it is in the nature of branches to produce reflection noise, and since it is in the nature of redundant circuits to increase reactance and capacity, the electrical characteristics of the semiconductor element are adversely affected. It is also necessary for the motherboard connecting electrodes 32 to be electrically isolated from one another. Accordingly, to produce the semiconductor element mounting interposer in an efficient manner, electroplating of the motherboard connecting electrodes 32 is followed by a process of making holes 37 in proximity to the motherboard connecting electrodes 32 so as to make the plated leads 33 as short as possible.
However, production of holes with a die produces flash around the edges of the holes, which can in some instances result in unacceptable appearance or impaired performance. In CSP production, the presence of holes on the circuit substrate tends to make resin encapsulation difficult. Further, the mechanical production of holes in a small CSP polyimide base film with good precision and without damage to the base film is not a simple operation. Also, considerable costs are entailed in die fabrication.